Watch for spider mites and thrips in late March and into April

Tom Dudek said greenhouse growers and scouts are seeing mites earlier than usual this year, with the most common problems being found on zonal and ivy geraniums, fuschia, New Guinea impatiens and spikes. Also, thrips activity is picking-up in some places.

Spider mites

Fortunately, we have some excellent miticides. When spider mites are found, spray the infested plants and plants nearby with one of the following products: Akari, Avid, Floramite, Hexygon, Judo, Kontos, Ovation, ProMite, Pylon, Sanmite, Shuttle-O, Suffoil-X ( concentrations > 1percent may be phytotoxic), Tetrasan, Kanemite.

Some of the miticides, like Hexygon, do not kill mites immediately, and it may take three to four days to see a difference. All of these products will reduce spider mite population for three to four weeks after a single application with the exception of Suffoil-X, a horticultural oil.


Late March and April is when thrips become more active in greenhouses. First, warmer temperatures and longer days give overwintering thrips the green light to reproduce. Second, an ample supply of pollen and warmer temperatures allow thrips to reproduce faster. Also, thrips present in greenhouse crops since February have now completed a second generation, turning 100 thrips into 30,000 thrips. This always comes as an unwelcome surprise in late April.

The best way to avoid problems with thrips is to watch the scouting reports carefully and begin your thrips management program when thrips numbers begin to increase on yellow sticky cards. When the number of thrips per yellow sticky card increases beyond your tolerance level (for most growers the threshold is from 10 to 100 per card), spray the infested greenhouse sections with one of the following products every five days for four applications. Conventional sprayers usually give better results than foggers. Obtaining good coverage of stems and the undersides of leaves improves control. High spray pressure and good air movement usually result in the best coverage.

Avid, Mesurol, NemaShield, Orthene 97, Overture, Pedestal, Pylon, Safari, Sanmite, Tristar, and Conserve. Note: thrips may be resistant to Conserve.

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